Beware of blue-green algae in livestock ponds

It could be a spectacular sunset scene looking at a pond with cattle grazing all around, but it could become a nightmare if blue-green algae invades the pond and wind up killing the livestock who water at the pond.

Jody Holthaus described what blue-green algae is and how it affects livestock during a recent Cattle Conversations webinar. Holthaus is the livestock and natural resources agent for the Meadowlark Extension district in northeast Kansas.

“For about five years, it’s really been a problem in my corner of Kansas,” she said. “I’ve been getting phone calls from producers that think they have it or have had sick or dead animals.”

Blue-green algae has been concerning, and she recently took part in a study with the veterinary diagnostic lab and helped collect and submit water samples.

“And, boy, that was a learning experience because some of the stock ponds had very toxic levels all summer and it never really changed,” Holthaus said. “So that’s really what kind of piqued my interest, and then some close friends of ours had cattle die, and trying to come up with answers for them that really got me interested in this topic.”

Blue-green algae is a group of algae that are cyanobacteria. It’s a photosynthetic bacteria that creates a “sort of photosynthesis,” according to Holthaus. There many different species of this algae, but the blue-green algae is the one that produces toxins that can be poisonous to people and animals.

“The toxins are in that cyanobacteria, and it holds it until it dies,” she said. “As it decomposes then it releases those toxins.”

The algae blooms can change the color of the water. Their buoyancy makes them float, often landing on the down wind side of a pond.

“It’s the most unnatural looking blue-green color,” Holthaus said. “It almost appears that someone has spilled some paint in your pond. And these usually will have smells associated with it.”

When temperatures increase, the wind blows, and there’s some rain runoff plus the sun warms the water causing an increased chance of getting blue-green algae.

“The causes of it are not completely understood, but we think it has to do with high phosphorus, high nitrogen and warming of the water temperatures,” she said.

Larger reservoirs tend to have blue-green algae every summer, but those farm ponds that are suspected of having it are often those where the grass surrounding it has been fertilized. But there are exceptions to the rule.

“But we also saw last summer a pond in the middle of the Flint Hills, that was a new pond that had rangeland that was not fertilized and it was one of the most toxic ponds that the vet lab had seen,” Holthaus said.

Some pond owners are confused about what a blue-green algae bloom looks like, and Holthaus gets more than her fair share of calls.

“They go out to their pond and they see some of this,” she said. “And I get these calls, ‘Oh, I think I have it.’ And a lot of this is just naturally occurring in ponds.”

Things like duckweed—a little floating plant—is already starting to form in ponds.

“It’s actually very high in protein, so if the cattle ingest this it’s a little supplement, I guess,” Holthaus said.

Then there’s normal pond scum, filamentous algae, among others. Some of the commonly occurring algae are confused with blue-green algae. So know the difference she said.

Sign up for HPJ Insights

Our weekly newsletter delivers the latest news straight to your inbox including breaking news, our exclusive columns and much more.

The most concerning aspect of cyanobacteria in blue-green algae is that it can cause reactions in humans. It could be a runny nose, rash, skin irritation and sore throat. When the cyanobacteria die, they release the toxins, and in humans it can show up as severe stomach issues, vomiting, diarrhea, liver damage and numbness in hands and feet.

“With pets and livestock it’s a staggering kind of weakness,” she said. “They have difficulty breathing, convulsions, vomiting and death, and it causes a sudden death if they’ve ingested enough of the toxic bacteria in in the water.”

Holthaus said a Kansas State University veterinarian once told her cyanobacteria is like cobra venom—there’s no cure.

“There’s no treatment, it’s just a sudden death,” she said.

A toxic bloom cannot be seen, and there’s really no way of knowing if it’s toxic, unless a laboratory test is performed.

“Our KSU vet diagnostic lab will do this for $22, and you can contact your extension agent or your veterinarian to get the water tested,” Holthaus said.

There is an at-home test people can do to determine if it is indeed a blue-green algae bloom. The Kansas Department of Health and Environment jar test is simple enough, she said. Fill a jar with a water sample from the affected pond from just below the surface of the water and don’t shake it up. Put it in the refrigerator over night and observe what happens.

“If the green algae sinks, then it is not blue-green algae,” she said. “But if it floats to the top, then you have blue-green algae.”

At this point it could just be blue-green algae or it could be toxic, but continued testing should be performed to determine if it is indeed blue-green algae.

“This whole procedure can be found on KDHE’s website,” she said. “They also have a stick test, but this one, I think, seems to be a little easier for producers to do.”

Holthaus said after several livestock deaths and high rates of toxicity, she began asking even more questions. In October 2019, she joined people from KDHE, the water office, the vet diagnostic lab, veterinarians and water quality specialists, among others.

“But we sat down around a table and discussed what we knew about it, what we didn’t know about it,” she said.

They discussed all the different things the literature says to do to treat the pond. One of the things that stuck out to Holthaus was traditional methods weren’t always the best choice.

“So we came up with some ideas on how we could mitigate these cons,” she said. “One of the things we had read was that barley straw put into a pond as it decomposes can help prevent blue-green algae blooms.”

The team was able to find some barley straw and located ponds that had previously been infected with blue-green algae.

“You don’t just throw this in there because you can kill fish by changing the oxygen level,” she said. “But the dosing rate is seven small bales per acre of surface water.”

The bales were staked down around the edge of the pond and kept about 20 feet apart with at least half the bale submerged. There was some flooding last year and knocked the bales out halfway through the season.

KDHE did the baseline water testing for the project and tested each month. Looking for poor nutrient profiles and all of the different toxins that might indicate blue-green algae, total chlorophyll and all of the algae that might be present.

“The COVID thing really kind of messed us up because their labs were dedicated to the COVID testing. So they outsourced this testing and they spent a lot of money on the testing, and we still don’t have all of the results back.”

The bales were installed in early May before anything bloomed, hopefully to get ahead of the curve.

“This isn’t a prevention, but it will kind of cut down on the algae,” Holthaus said.

As the bales decompose it releases polyphenols and other chemicals that retard the growth of the blue-green algae.

So the factors that can determine whether this works is the dilution of the water, any of the algae species that are already present, and other factors like flooding, for instance,” she said.

Holthaus believes once their results are received, they’ll be able to better help producers and veterinarians who have to deal with these sick animals. Communication with all those involved in cases where animals are poisoned by blue-green algae is important.

“It’s kind of a hidden problem,” she said. “But if you know you have it in your pond it’s really worrisome for the producer because you know that you have this wonderful pond out there that you’d like to water out of and then the water is not good.”

For more information about blue-green algae visit

Kylene Scott can be reached at 620-227-1804 or [email protected].